Binary Search Template Leetcode, The meaning of it? - binary-search

Question

I Found a Binary Search Template here in leetcode
def binarySearch(nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: int
"""
if len(nums) == 0:
return -1
left, right = 0, len(nums)
while left < right:
mid = (left + right) // 2
if nums[mid] == target:
return mid
elif nums[mid] < target:
left = mid + 1
else:
right = mid
# Post-processing:
# End Condition: left == right
if left != len(nums) and nums[left] == target:
return left
return -1
They say that "Template #2 is an advanced form of Binary Search. It is used to search for an element or condition which requires accessing the current index and its immediate right neighbor's index in the array."
I am struggling to understand what the information above means. In a usual binary search right would be
right = len(nums) - 1 # before while loop
right = mid - 1 # inside while loop
and the while loop would be
while left <= right:

Answer 1

You are performing a binary search on an array.
Lets say the array has 100 elements.
# left, right = 0, len(nums)
left = 0, right = 99
# mid = (left + right) // 2
mid = 49
# elif nums[mid] < target:
We need to move right.
# left = mid + 1
left = 50 and right = 99
# else:
We need to move left.
# right = mid
Left = 0, right = 49